A microprocessor based Remote Multiplexer Terminal (RMT) is presented which includes redundant central processor units for improved reliability.
The use of redundant Central Processor Units (CPU's) can eliminate the single point failure modes found in prior art systems. Prior efforts to provide redundancy have not always been successful because of the difficulty of avoiding a single point of failure somewhere between the CPU and the input/output (I/O) subsystem. The potential for a single point of failure often involves the failover switch circuitry which transfers the signal processing from one subsystem to the other. In prior art systems the complexities involved in making it possible for two devices to control a single input/output device have often precluded making a completely redundant system.
With our invention, the single point of failure is avoided. A concept is introduced which allows two devices to control a single output by moving the switching circuitry from between the CPU's and the I/O subsystems to a point very close to the actual I/O device interface. Software instructions are programmed in to insure correct operation with failover occurring quickly and without loss of data.